The use of implantable medical devices to treat a variety if diseases is growing due to the rapid advances in technology. Diseases that disrupt the ability of the heart, brain, or nervous system to communicate or function normally include heart rhythm disorders such as ventricular fibrillation, heart block, and neurologic disorders such as epilepsy, multiple sclerosis, spinal injury, and dysautonomias. Drug and pharmacologic therapy have been used to treat these disorders, and pacemakers and defibrillators have been used to treat heart rhythm disorders. As shown in U.S. Pat. Nos. 5,351,394, 5,215,086, 5,188,104, 5,154,172 and 5,707,400, treatments for deep brain stimulation include the use of wires within the brain with implantable devices to stimulate target areas of the nervous system in order to control epilepsy, hypertension, as well as movement disorders such as Parkinson's disease.
Surgical procedures have also been used to treat these disorders. For example, open brain surgery for the placement of leads such as wires that are positioned through brain tissue to reach target sites that are tunneled under the skin to a device implanted elsewhere: and placing wires in the heart to provide a defibrillation shock (established procedure) using the blood vessels as the conduit to reach the heart.
The mode of brain and heart regulation via electrical impulses has been well known for decades and is the basis for today's pacemakers, defibrillators, and deep brain stimulation devices, as mentioned in the above referenced patents. Defibrillation and cardioversion are techniques employed to counter arrhythmic heart conditions including some tachycardias in the atria and/or ventricles. Fibrillation is a condition where the heart has very rapid shallow contractions and, in the case of ventricular fibrillation, may not pump a sufficient amount of blood to sustain life. A defibrillator often is implanted in the chest cavity of a person who is susceptible to reoccurring episodes of ventricular fibrillation. Typically, electrodes are employed to stimulate the heart with electrical impulses or shocks, and are of a magnitude substantially greater than the magnitude of pulses used in cardiac pacing. The implanted defibrillator senses a rapid heart rate during fibrillation and applies a relatively high energy electrical pulse through wires connected to electrodes that are in turn attached to the exterior wall of the heart.
Examples of ECG sensors are shown, for instance, in U.S. Pat. Nos. 6,412,490 and 5,987,352. Examples of pacemakers are shown, for instance, in U.S. Pat. Nos. 3,554,187; 3,760,332; 3,842,842; 4,248,237; and 4,124,029. The technologies described in those patents are, however, hampered by the use of a transvenous lead for electrophysiologic stimulation. In those technologies, a transvenous/vascular access is required for intracardiac lead placement. Those technologies are also susceptible to an acute risk of cardiac tamponade, perforation of the heart or vasculature and long term risk of endocarditis or a need for intracardiac extraction of the lead due to failure. Also, current technologies present a problem for intracardiac defibrillation implantation in younger patients or in patients who are otherwise not candidates for the implantation because of anatomical abnormalities. Complex steps and risks are involved in obtaining venous vascular access and placement of the transvenous lead in the patient population requiring defibrillation.
Delivering electrical sensing and stimulation leads to specific areas of the brain is difficult. The skull must be opened and the brain exposed, the leads are then inserted through normal brain tissue in order to reach the abnormal section, and then the leads are tunneled under the skin often to the chest are where a device is connected to the lead(s). The risk of infection is high because of the resultant contact of the inner brain areas with areas close to the surface of the skin via the lead. In addition, normal brain tissue is disrupted in the process, and any complication or infection often requires that the whole implanted system be removed.
Given the risks associated with these current procedures, aa well as the limitations that arise when devices must use a lead to reach the target site, there is a need for a new approach using implantable electronic medical devices that are wireless for the treatment of heart, brain, and nervous system disorders.